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Phone available May 29 in Europe, in Asia and the United States this summer

Samsung has launched its Galaxy S III smartphone, which it hopes will help solidify the company as the leading challenger to Apple and its iPhone 4S.

The new handset, with a whopping 4.8-inch screen and an 8-megapixel camera, was unveiled at a slick launch party in London on Thursday, complete with a backing orchestra.

Billed by Samsung as having been "designed for humans," the phone features voice and eye-recognition technology that the company hopes will set the handset ahead of its rivals in the crowded smartphone market.

Samsung has overtaken Nokia as the world's best-selling mobile phone maker, and Juniper Research reported Tuesday that Samsung also overtook Apple in smartphone sales in the first quarter, in what it described as "increasingly a two-horse race."

The new Galaxy handset, which runs the most up-to-date version of Google's mobile operating system -- Android 4.0 Ice Cream Sandwich -- recognizes when a user is looking at it, and ensures the screen doesn't go dark while it has eye contact.

Samsung -- a sponsor of the Olympics -- revealed it will be sending devices enabled with mobile payment technology to the 2012 games in London.

Chris Hall, editor of technology website Pocket-lint, said he was "pleasantly surprised" by the new phone.

"When you compare it to the nearest rival it feels like they have pulled off a bit of a trick," he said. "They have put some effort into software innovations, particularly the eye recognition. The voice recognition feels like a reaction to Siri on the iPhone, but I don't know many people who actually talk to their phones."

"I think the success of the Galaxy S II proves people want something different that isn't an iPhone, and I think the S III is a valid successor to the S II." Samsung said the phone will be available in Europe on May 29, followed by launches in Asia, Africa and Latin America. A 4G version will go on sale in North America, Japan and South Korea in the summer.